I am trying to build a field charger for my drone batteries.

GopherT

Joined Nov 23, 2012
8,009
Powering things of high current draw is sometimes difficult. Before going solar, check if there are other options...


Step 1) fly near a current bush.



Step 2) make sure the current bush is high enough amperage
Step 3) look for the outlet in the current bush (sometimes hard to find)
upload_2016-6-20_17-2-23.png

Step 4) plug in an enjoy
 

Thread Starter

Hamish McLagan

Joined Jun 17, 2016
16
Powering things of high current draw is sometimes difficult. Before going solar, check if there are other options...


Step 1) fly near a current bush.



Step 2) make sure the current bush is high enough amperage
Step 3) look for the outlet in the current bush (sometimes hard to find)
View attachment 108005

Step 4) plug in an enjoy
Hmmm can't say I've ever come across one of those but I'll keep an eye out!!
 

Kermit2

Joined Feb 5, 2010
4,162
If you want a max of 5 amp for charges then 1.5 to 2 amps should work.
If you want to draw 5 amps continuously until the batteries are charged then you need 4 or more amps from a panel.
Check the c web for wholesale solar panel dealers. Some only deal in pallet loads but several offer single panels.
190 watt panel for 165 US was one deal I spotted.
45 to 60 watts should fit your needs
 

Thread Starter

Hamish McLagan

Joined Jun 17, 2016
16
https://www.amazon.com/dp/B01H4245QG?psc=1

Here is one that would be perfect and gives almost 6 amps
Hmmm chunky. Was hoping for something about 300mm square. Lipo's take about 40mins to charge each with starting amperage 5A. If parallel charging 2 lipo's takes about 50-60mins starting amperage 5A. This is when charging from wall socket. Would like to replicate those times from sla's. Would changing to a deep cycle battery make a difference?
 

ronv

Joined Nov 12, 2008
3,770
Hmmm chunky. Was hoping for something about 300mm square. Lipo's take about 40mins to charge each with starting amperage 5A. If parallel charging 2 lipo's takes about 50-60mins starting amperage 5A. This is when charging from wall socket. Would like to replicate those times from sla's. Would changing to a deep cycle battery make a difference?
I think your problem is that a 7AH battery isn't really 7AH at the currents you would like. Below is an example:
upload_2016-6-21_19-29-22.png
If money is no object a big lipos would work better. Or as you mentioned a larger capacity deep cycle.
 

dougp01

Joined Dec 6, 2005
31
One very important thing. It is almost always a bad idea to parallel batteries. If one battery is off in voltage by even 1/10th of a volt, you will get cross charging currents. That is the battery with the higher voltage will attempt to charge the parallel battery and the amount of current is limited only by the internal impedance of the batteries themselves. While the two batteries will eventually equalize to the same voltage, it's never a good thing to circulate these currents between the two.

In order to prevent this problem, it is common to place a steering diode in series with each battery. This will allow charging current to flow into the battery but not between the two batteries. Of course, this also means you now have a voltage deficit of 0.6V that the charger needs to make up.

Good luck, Doug
 

ronsoy2

Joined Sep 25, 2013
71
Hi!
Our RC club had the same problem. Too far to walk from the parking lot to use the car battery. We got one of these: ebay 282077353317. We can have 2 to 4 people charging at one time at quite a heavy charge rate. Forget the storage battery idea. You will be frustrated at how big and heavy of a battery you need!
 

GopherT

Joined Nov 23, 2012
8,009
If one battery is off in voltage by even 1/10th of a volt, you will get cross charging currents.
While the two batteries will eventually equalize to the same voltage, it's never a good thing to circulate these currents between the two.
Doug,

Do you have any documentation on this statement that a 0.1V delta is too much current to allow self-balancing?

My thoughts are that a big lithium battery generally has no less than 0.05 to 0.1 ohms of internal resistance so a 0.1V difference in battery voltage results in a 1 to 2 amp current flow until the charges are balanced. Surely a large lithium battery can handle a 1 to 2 amp current flow if they can handle 40+ amps of peak flow.
 

Thread Starter

Hamish McLagan

Joined Jun 17, 2016
16
Hi!
Our RC club had the same problem. Too far to walk from the parking lot to use the car battery. We got one of these: ebay 282077353317. We can have 2 to 4 people charging at one time at quite a heavy charge rate. Forget the storage battery idea. You will be frustrated at how big and heavy of a battery you need!
I hear what you're saying but I'm after a compact and as light as possible way to recharge my lipo's.
Plan on going bush with my gear at some stage and its either this or a heap of lipo's
 
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